Saket talked about a real-work scenario where PO adds more acceptance criteria to a user story during a demo. I would like to know how will this be addressed:a) would we create a new user story with the new acceptance criterias and mark the current story Done ?b) or we move this story to next Sprint with additional criteria added to it.c) or any other way

Acceptance criteria are added to a particular user story. You can move this story to the product backlog with additional criteria added to it. Based on priority, in Sprint planning meeting, a new set of user stories will be selected